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-   -   A new fully analog FM modulated wideband optical transport Open Standard. (http://www.diyaudio.com/forums/analog-line-level/223044-new-fully-analog-fm-modulated-wideband-optical-transport-open-standard.html)

freax 7th November 2012 08:19 AM

A new fully analog FM modulated wideband optical transport Open Standard.
 
Read post #36 and then forwards from this thread:
http://www.diyaudio.com/forums/tubes...ml#post3230168

Important posts are:
http://www.diyaudio.com/forums/tubes...ml#post3230185

http://www.diyaudio.com/forums/tubes...ml#post3231390

http://www.diyaudio.com/forums/tubes...ml#post3231674

http://www.diyaudio.com/forums/tubes...ml#post3231684

I'm hoping that the diyaudio community can collaborate and construct some kind of working prototype, which will then spur further development later on for higher analog bandwidth over fiber optic cabling.

So people will

#1, Have a way of optically isolating their TT or DAC's from their amplfiers and transport those low level signals over from one part of the room to the other with little loss or degredation of the signal by placing that low level analog signal onto an optical fiber.
#2, Do away with the expensive cable industry once and for all, much like how Optical TOSLINK has done for home consumer grade audio.
#3 And finally retire the somewhat unpredictable RCA connectors, even though RCA is great and all, and even works for RF on the HF bands, I think we should develop a new optical transport interconnect, you never know it might turn out to be half good.

Base it upon a currently existing connector so adoption is widespread, Some suggestions are (for stereo) a pair of LC/SC or ST (Bayonet fiber connectors), or a pair of TOSLINK connectors. Each carrying 1 High quality mono channel or 2 lower quality mono channels for 2 or 4 channel analog.

HJWeedon has made it pretty clear already that this should be an FM modulated standard, with a 200kHz carrier deviation. And as we all know FM can easily carry Stereo, so catering to the 5.1 or 7.1 crowd shouldn't be too difficult.

The astronomy/physics community is already doing it: http://www.skatelescope.org/public/2...umentation.pdf

So why not us?

Here is a few more interesting links to look over:
http://electronics.stackexchange.com...r-laser-driver
http://www.ilxlightwave.com/appnotes...r%20Diodes.pdf
http://www.its.caltech.edu/~atomic/p...controller.pdf

TV7 7th November 2012 08:27 AM

This should be interesting, although my thread has a more catchy title;)

freax 7th November 2012 09:41 AM

ok ok, I'll give it a shorter name, how about analog laser-based open sound interface or ALOSI

My contribution to this idea has ended, I'm far too unwise to be contributing to this thread and I hope some smart sparks will come along and make it a reality with a working prototype, then publish the schematics.

I certianly hope the same thing doesn't happen as has happened in the other thread over. And by this I'm referring to "A New Interconnect Design".

Its been a long time coming thats for sure. and by that I mean this project.

DF96 7th November 2012 10:50 AM

Sounds completely barmy to me. You want to include a highly linear analogue FM or pulse-width modulator and corresponding high quality demodulator for every interconnect? Every line stage becomes an FM tuner? Have you ever designed an FM tuner? What is wrong with a bit of copper cable?

You will never do away with the expensive cable industry, because such purchases are not based on need but perception. If your idea got off the ground then within a few months people would start offering expensive fibres for it. That is human nature.

HJWeedon 7th November 2012 02:55 PM

Hello.

First we have to identify the customer. Is this going to replace cable? My answer would be NO. Copper cabling works pretty well. It is only when there are significant AC ground-loop problems that we have to do away with the copper connection.

In my own case, this was primarily due to the shortsighted Ground. Neutral and Hot wiring of incoming power. This system is inherently unbalanced, capacitive and inductive coupling introduces 50/60Hz hum in every wire. In my own case I installed an isolation transformer where the output is 2 X 65V AC. The center-tap of the isolation transformer is connected to GROUND. This power configuration gives about 20dB lower sensitivity to line frequency HUM.

But that is not what we have set out to do.

A suggestion has been made to use 98MHz carrier I.E. right in the middle of the FM band.
Why do that? is that so all our neighbors can listen in on their FM receiver? I do not like this choice for that reason.

My selection would be: 2MHz to avoid interference in the standard AM band, and not in the way of Amateur radio which is generally located at harmonics of 3.5MHz. The 2MHz wiring is low enough so that regular wiring technique can be used. Also circuit design can become relatively mundane.

My second choice would be 10.7MHz where a plethora of circuits exist off the shelf. This is the standard FM IF frequency.

My third choice would be 60MHz in the RF-"no-mans land" second harmonics is 120MHz etc not disturbing anyone.

10.7MHz would require some careful wiring, but not excessive. 60MHz would require solid state and printed circuit-board technology. An experienced constructor could handle any frequency, but the less experienced builder would have to limit himself to the 2MHz circuit techniques.

That is all for now.

Hans J Weedon.

Frank Berry 7th November 2012 03:04 PM

"My third choice would be 60MHz in the RF-"no-mans land" second harmonics is 120MHz etc not disturbing anyone."

120MHz is aircraft communications.

dmills 7th November 2012 07:12 PM

Insane idea, FM even with very wide deviation introduces distortion (It has to, you have to band limit the bessel sidebands somewhere), and FM discriminators are not exactly distortion free, that is before you consider that you have just doubled the number of parts in most consumer audio kit to no benefit.
Hideously complex compared to just doing a properly thought out balanced interface, which will NOT hum if both ends are implemented even mostly competently (Even an unbalanced interface will usually be perfectly acceptable given line lengths typical of HIFI usage).

Hell, if you want optical, SPDIF or ADAT are both simpler to implement than this monstrosity, or do a simpler delta sigma modulator at the transmitter and a low pass filter at the receiver.....

Moving line level audio over HIFI sort of distances is very nearly electrically trivial, and doing the same over hundreds of meters of twisted pair is only a little tougher, it does not really take anything except competent line drivers and receivers.

Sorry, but I don't buy there being any problem with sending raw baseband for most audio applications (Certainly including all HIFI uses), the fact that some folks cannot design an audio input or output stage that works properly should be taken as a sure indication that the same folks cannot design high speed FM discriminators. Design your kit right and more or less any old bit of twisted pair (Ideally with a screen but you can often get away without) will do just fine for moving audio around.

Regards, Dan.

DF96 7th November 2012 07:46 PM

2MHz wideband FM could affect the 160m amateur band.

10.7MHz has the advantage of using existing circuits and components. Still a daft idea, though. People who can't build a decent audio interface won't be able to build RF stuff either.

HJWeedon 8th November 2012 05:24 AM

Gentlemen.

Dan (dmills) is actually quite correct, the simplest interconnect is in all honestly the wired connection. It is just that the circuit designer buried deep inside us wants to get out and do something complicated and tricky. My preference for interconnect under reduced circumstances would be an Ethernet type of cable. This cable has 4 well twisted pairs and a convenient locking connector. Each channel gets its own cable where all 4 pairs are connected in parallel.

We drive this cable with about 100 Ohm source impedance to limit capacitive hum pickup. the receiving end should be a high quality differential receiver circuit with about 40dB of common mode rejection (1% resistors, obviously). The signal level should be about 3V nominal full scale, not the More "modern" 1V full scale. I pick 3V (RMS) because that is 18V in the very highest peaks (6* RMS to account for the unfortunate sum of several instruments playing full blast) This can be done to high performance with +/- 20V rails on the driver and receiver side. The load impedance at the receiver end should be be in the 22 to 47k range, mainly to limit the thermal noise of the load resistor.

This interconnect is simple and has, believe it or not, already got gold plated connection points as part of the definition. Since we plan to put 4 pairs in parallel we have great redundancy for continuously reliable interconnections.

For the freak among us this cable also comes in a more expensive shielded variety.

Anyway, this is how I plan to connect up my remote signal processor to my living-room signal sources. My listening room is 11*11m and the speakers are in one end of the room and the source equipment in the other end. I can not put the speakers next to the source equipment because that is where the piano and the book-cases are.

I can not put the Audio equipment near the speakers because there is a kitchen and a bathroom there. Instead of rebuilding the house, I prefer the less expensive way of rewiring the Audio equipment.

Years ago I had my Audio system closer to the speakers but every time the electric water-heater turned on I had induced hum in the audio channels. That turned out to be the power-feed to the house magnetically inducing objectionable hum in the Audio system.

Wife acceptance is also important, heavy shielded cables across the floor, simply does not fly.

Well that is my reality, guys.

Hans J Weedon.

freax 8th November 2012 09:10 AM

Haha.

I initially suggested AM modulation, but then I adopted HJWeedon's FM idea because it made sense if we're going to be using fiber, and he knows better. And even on Laserdisc I truly did love the sound that the FM tracks put out, especially when they were played back on Tube equipment.

And the main reason why I suggested that we use 98Mhz was because people out there in the field can protect their neighbours by simply using an FM radio that they might have handy inorder to better shield their circuits. If these circuits are leaking /at all/ then there is something seriously gone wrong.

As far as I understand it all we need to do is produce a carrier modulator which will make its way into a laser diode, whatever the frequency is, and then modulate that modulator with an FM modulator with an IF of some ungodly low number. so all of that could be on the order of 0.005 watt of RF, tops, and it would be heavily shielded.

But if we are going to go back to a very wideband AM modulated signal then I strongly suggest that you keep away from 1.6MHz-30Mhz and instead either take it down to 1MHz or straight up to 98MHz. The shortwave bands are extremely sensitive to even microscopic amounts of wattage, hence the whole invention of the QRP crowd. and they /will/ come down on us like a ton of bricks.

Think about it this way, if we put the carrier on a band that isn't a Broadcast Band, and someone who is building their kit out there in the field all of a sudden has a bias resistor out of specification, then all of a sudden you've got anywhere from a petawatt to 1 watt of RF spattering itself all over a critical government or corporate infrastructure.

And that my friends would be utter disaster to this project.

Remember this line, the RF bands are already chock full of every single service you could imagine, there is no point in finding a free part of the spectrum because you have to take into account every single country in the world, the only bands that we could conceivably use are the ISM bands. Either that or 455KHz. or the BCB's, because 1 Mhz and 98Mhz are both internationally known as broadcast bands /and/ people can self-diagnose their circuits without any understanding or knowledge of how to use a HAM radio or a Shortwave radio.


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